This invention relates to a novel self-brazing aluminum laminated structure as well as to a method of making the laminated structure and a brazed product.
It is common practice to join aluminum components by disposing an aluminum brazing alloy between or adjacent the component surfaces to be joined, and heating the brazing alloy and the joining surfaces in appropriately assembled fashion to a temperature (brazing temperature) at which the brazing alloy melts while the components remain unmelted. Upon subsequent cooling, the brazing alloy forms a filet or joint that bonds the joining surfaces of the components. For assured selective melting of only the brazing alloy in the heating step, it is commonly preferred that the melting point of the brazing alloy be at least 30.degree. to 40.degree. C. lower than that of the metal of the components. An example of a typical aluminum brazing alloy is an aluminum-silicon eutectic composition, which starts to melt at about 577.degree. C.
Wadsworth, U.S. Pat. No. 936,389, issued Oct. 12, 1909 describes a process for modifying the surface of a metal substrate by making projections or depressions in the surface and during this operation adding finely divided material such as carbon, vanadium, nickel, zinc, etc. which is incorporated or alloyed with the surface, which, because the substrate metal is quite soft and plastic, will be forced into the metal and thoroughly mixed and thus quickly and readily combine or alloy therewith. He also teaches that after the incorporation of the particles into the surface bearing the projections and depressions, the shape must be sent to one or more smoothing passes to reduce the area of the marked surface, thereby resulting in a substantial densification of the surface and imparting improved corrosion and abrasion resistance.
DiFrancesco, U.S. Pat. No. 5,083,697 and W091/12108, published Aug. 22, 1991, describes a method of joining metal surfaces by elasto-plastic deformation in which at least one of the surfaces bears metallized particles which contain a core of hard material which is harder than the materials to be joined so that as the surfaces are pressed together there is elasto-plastic deformation of the surfaces in contact with the hard particles which will lead to diffusion bonding of the surfaces. Among the materials that may be bonded are mentioned aluminum, silicon, copper, lead, tin and their alloys.
Gal, U.S. Pat. No. 4,601,089, issued Jul. 22, 1986, refers to a procedure in which zinc powder is rolled into an aluminum surface whereby the zinc-coated surface becomes solderable. In accordance with the Gal procedure, one surface of the aluminum must be fully coated with the zinc in a thickness which enables it to be soldered without burning through the layer. This requires a thickness in the order of 1/10 mm.
Mori, U.S. Pat. No. 4,365,995 relates to the production of powder layers 10 to 20 .mu.m in thickness, consisting largely of aluminum, onto steel surfaces by rolling. The rolled in powder is sintered at 280.degree.-520.degree. C. and the purpose appears to be for modifying the surface.
Morishita et al, U.S. Pat. No. 4,848,646 describes an electrochemical technique for depositing zinc and nickel to generate a solderable surface on aluminum.
It is the object of the present invention to produce a brazing sheet in the form of a laminate in which the brazing sheet carries both a brazing flux and a metal capable of forming in situ a eutectic alloy with an aluminum substrate when the sheet is heated.